The invention relates to a transformer which comprises:
a coil carrier with a hollow coil tube which has a first flange and a second flange;
a primary coil and a secondary coil around the coil tube between the first flange and the second flange;
high-voltage contacts at the second flange in connection with the primary coil;
low-voltage contacts at the first flange in connection with the secondary coil;
a magnetic flux conductor in, laterally of, and transverse to the coil tube;
a first portion of the magnetic flux conductor which extends transversely to the coil tube being accommodated in a trough-shaped holder with ends, which holder is integral with the first flange; and
the low-voltage contacts extending transversely to the coil tube and transversely to the trough-shaped holder.
Such a transformer is known from WO 97/05632.
In the known transformer, a magnetic flux conductor is formed by an E-shaped core which is present inside and laterally of a coil tube and which cooperates with an I-shaped core which extends transversely to the coil tube and is present in a trough-shaped holder. A comparatively thick insulation layer around the primary or around the secondary coil is necessary for obtaining a safeguard against electrical breakdown between the primary and the secondary coil in accordance with a generally accepted safety standard. It is usual in these transformers to provide this comparatively thick insulation layer around the secondary coil, which is present at the low-voltage side. The secondary coil in this case consists of, for example, triple-insulated wire. This secondary coil has fewer turns than does the primary coil, so that the cost of this insulation layer can remain limited. The primary coil in this situation has a comparatively low insulation value, so that a breakdown will occur between the primary coil and the cores if an overvoltage should arise on the high-voltage contacts at the high-voltage side of the transformer. These cores, accordingly, form part of the high-voltage side in the case of any breakdown.
A disadvantage of the known transformer is that the high-voltage side is not securely separated from the low-voltage side. A breakdown from the primary coil to the cores involves the risk of breakdown from the high-voltage side to the low-voltage side because the low-voltage contacts, which belong to the low-voltage side, are present adjacent the cores, which belong to the high-voltage side. When these transformers are used in a circuit, therefore, the safety of operators handling this circuit with transformer is not guaranteed. In addition, there is a risk of damage to further electrical components in the circuit which are in connection with the low-voltage contacts because high-voltage is capable of reaching the low-voltage side of the transformer.
It is an object of the invention to provide a transformer of the kind mentioned in the opening paragraph in which the high-voltage side is separated with a high degree of security from the low-voltage side.
According to the invention, the above object is achieved by the transformer which is characterized in that the first flange has a first extension that extends away from a first side of the coil tube along the low-voltage contacts The first flange also has a second extension extending from a second side of the coil tube, where the first side is opposite the second side. The first extension is longer than the second extension. The first flange thus forms an additional electrical separation between the magnetic flux conductor and the low-voltage contacts. This forms a so-called clearance distance where the first flange constitutes a comparatively long distance for arcing through the air between the magnetic flux conductor and the low-voltage contacts. Further, a comparatively long creepage path is also formed between the magnetic flux conductor and the low-voltage contacts. The creepage path is the shortest path along which a current, a so-called creepage current, can flow along material which is present between the magnetic flux conductor and the low-voltage contacts. The creepage current flows along the surface of the material as a result of, for example, pollutants and moisture present on the material and is dependent on the type of synthetic resin of the material. Since the first flange forms a comparatively long clearance distance, no arcing through the air can take place between the magnetic flux conductor and the low-voltage contacts, given usual values of overvoltages. In addition, the lengthened flange forms a comparatively long creepage path from the magnetic flux conductor along the surface of one side of the flange, over the edge and along the surface of the other side of the flange, along the surface of the holder to the low-voltage contacts of the transformer.
In one embodiment, a wall transverse to the first flange is present at each end of the trough-shaped holder and also at the first flange. The wall extends along the low-voltage contacts. This renders it possible for the low-voltage contacts to be present close to the ends without a comparatively short creepage path from the low-voltage contacts to the magnetic flux conductor being caused thereby.
In a further embodiment, the wall, seen transversely to the first flange, extends to beyond the trough-shaped holder.
An additional embodiment of the transformer according to the invention is characterized in that the coil tube has a rectangular cross-section with an opening at each of two mutually opposed sides. Through the openings, a better thermal contact is obtained between the coils, which are wound around the coil tube, and a portion of the magnetic flux conductor present in the coil tube. This is favorable for the removal of heat generated in the coils and the portion of the magnetic flux conductor present in the coil tube.